1. Field of the Invention
The present invention relates to wireless communication, and more particularly, to a method and an apparatus for acquiring initial synchronization using a relay-amble in a wireless communication system.
2. Related Art
The institute of electrical and electronics engineers (IEEE) 802.16e standard has been adopted as a title of ‘WMAN-OFDM TDD’ as a sixth standard for the international mobile telecommunication (IMT) 2000 in the ITU-radiocommunication sector (ITU-R) under the international telecommunication union (ITU) in 2007. The ITU-R has prepared the IMT-advanced system as the next generation 4G telecommunication standard after the IMT-2000. The IEEE 802.16 working group (WG) has determined the progress of the IEEE 802.16m project for the purpose of making an amendment standard of an existing IEEE 802.16e as a standard for the IMT-advanced system at the end of 2006. As seen from the above purpose, the IEEE 802.16m standard involves two aspects of the continuity of the past which is the amendment of the IEEE 802.16e standard and the continuity of the future which is a standard for the next generation IMT-advanced system. Therefore, the IEEE 802.16m standard needs to satisfy all the advanced requirements for the IMT-Advanced system while maintaining compatibility with the IEEE 802.16 standard based mobile WiMAX system.
Recently, a wireless communication system including a relay station (RS) has been developed. The relay station serves to increase a cell coverage and improve transmission performance. A base station serves a mobile station positioned at a coverage boundary thereof through the relay station, thereby making it possible to increase the cell coverage. In addition, the relay station improves reliability of signal transmission between the base station and the mobile station, thereby making it possible to increase transmission capacity. Even though the mobile station is in the coverage of the base station, in the case in which the mobile station is positioned in a shadow area, the relay station may also be used.
A preamble is a signal transmitted from the base station in order to perform initial synchronization between the base station and the mobile station. The mobile station detects an autocorrelation signal using repetitive characteristics of the preamble received from the base station and search a peak of an output of the autocorrelation signal, thereby making it possible to search a start point of a frame. When the mobile station searches the start point of the frame as described above, it may generate time division duplex (TDD) switch signals of downlink (DL) and uplink (UL) periods based on the start point of the frame. Since the base station recognizes a reference time in advance and performs downlink transmission according to the reference time, it needs not to again search the start point of the frame.
In the case in which the relay station is introduced, a relay-amble (R-amble) may be additionally transmitted, in addition to the preamble. The reason is that a frame structure in the case in which the relay station is introduced may be different from that of a frame of an existing wireless communication system. However, a method for acquiring initial synchronization using a relay-amble has not yet been discussed.
Therefore, a method for efficiently acquiring initial synchronization using a relay-amble in a wireless communication system into which a relay station is introduced has been demanded.